Ink jet printers eject ink onto a print medium through one or more print heads in a controlled pattern of closely spaced dots. Black or color images may be formed. The print heads are each supplied with a different color ink to form black and color images. For example, an ink jet printer may include reservoirs of cyan, magenta, yellow, and black inks.
The reservoirs of ink may be attached to the print heads. These reservoirs may take the form of header tanks that receive ink from corresponding bulk containers, or standalone cartridges.
It is desirable to detect the level of ink in the reservoirs to ensure a proper supply of ink to the print heads. For instance, when the ink reservoirs are in the form of header tanks, it is desirable to trigger refilling of the header tanks from their corresponding bulk supplies when the level of ink in the header tank reaches a predetermined threshold level to ensure a continuous supply of ink to the print heads. When the ink reservoirs are in the form of cartridges, it is desirable to detect the level of ink within the cartridges to allow the user to be notified when the level of ink within the cartridges has reached a predetermined threshold level, so that the cartridges can be replaced before the ink supply is exhausted.